The invention relates to a process for producing high strength, high shrinkage nylon 66 filament yarn for industrial fabrics, especially airbag fabrics, by multistage drawing of polyamide 66 LOY by means of at least three heatable draw roll units or godet duos and direct winding up of the drawn yarn to form a cylindrical yarn package, specifically a cheese, and to nylon 66 filament yarn.
High shrinkage thermoplastic filaments are typically wound onto cops with a protective twist suitable for the further processing. The disadvantage of winding onto cops is that the maximum winding speeds are only of the order of a few hundred metres per minute. A further disadvantage of winding onto cops is that the yarn capacity of a drawn cop is generally limited to about 4 kg of yarn. Economical yarn manufacture is no longer guaranteed after such a process. It would be desirable to wind high shrinkage yarns directly onto cylindrical bobbins. However, it has hitherto not been possible to wind thermoplastic polymer yarns possessing high hot air shrinkage. Such yarn has to be wound up under relatively high tension in order that an undesirable reduction in the hot air shrinkage may be prevented. This has serious disadvantages for the package build. The high yarn tension creates such high radial forces within the cross-wound package that, on the one hand, the package centres are deformed, so that the full package cannot be removed from the mandrel of the winding machine. A further disadvantage is, on the other hand, that unacceptable winding deformations are observed, which make it impossible to build full packages.
DE-A-34 37 943 discloses a process for producing nylon 66 filament yarn wherein an undrawn yarn of polyhexamethyleneadipamide having a relative viscosity of 60 to 100 in formic acid is drawn in one or two stages. The apparatus suitable for this purpose consists of a plurality of heated draw roll units. To improve the drawability of the yarn additional heat sources in the form of contact heaters are provided between the draw rolls. It is known that, in the melt-spinning process, at a winding speed of 4500 m/min and higher, the winding tension is so high that it is no longer possible to remove a paper centre from the winding machine. The problem is solved in this process by relaxing by about 10%. Nothing is said about the winding of the drawn yarn. The known yarns are wound up at speeds of not more than 20 m/min. The aim of the known process is the production of dimensionally stable filament yarns for tyre cord fabrics, possessing high strength, high elongation and low shrinkage, ideally below 5%. The drawing conditions and especially the winding conditions onto cheeses are optimized for these yarns.
Lately, however, airbag fabrics specifically are increasingly produced using yarns having high hot air shrinkage. It is true that such yarn types are easy to produce, but they are difficult to wind onto cheeses.